Photolithography is commonly utilized to form microstructures, with exemplary microstructures being integrated circuit devices and Micro-Electro-Mechanical Systems (MEMS). Photolithography utilizes patterned electromagnetic radiation (typically ultraviolet light) to create a desired pattern in a photosensitive material (photoresist).
In typical processing, photoresist is coated on the substrate, and electromagnetic radiation is passed through a patterned mask (typically called a reticle) to form a pattern of exposed and unexposed regions of the photoresist. The photoresist is then developed to selectively remove either the exposed or unexposed regions. If the exposed regions are removed, the resist is referred to as a positive resist; and if the unexposed regions are removed, the resist is referred to as a negative resist.
The patterned resist can subsequently be utilized as a sacrificial mask for patterning layers underlying the resist. Alternatively, the patterned photoresist can be a non-sacrificial material utilized as an element of a microstructure.
A continuing goal is to decrease the dimensions of microstructures. It is desired to form patterns in photoresist with ever-increasing accuracy as the desired sizes of microstructures continue to shrink, and this is creating difficulties with present photolithographic techniques.
An exemplary application for photolithography is to form patterns in upper layers of materials that are desired to align with patterns in underlying layers. For instance, in semiconductor manufacturing it is often desired to establish vertically-extending electrical connection between upper conductive structures and lower conductive structures. As device dimensions decrease, this becomes an increasingly difficult challenge. Alignment tolerances are now approaching nanometer dimensions.
At the tight tolerances of present-day manufacturing, misalignment of photolithographically-formed patterns in upper layers relative to structures in lower layers is common, and accordingly numerous procedures have been developed for addressing misalignment problems.
One method is to avoid photolithography, and to instead use self-aligned-contact methods where the selectivity of different materials to different etch chemistries is used to pattern materials. Such methodology can be useful in particular circumstances, but creates problems in developing appropriate etch chemistries, development times, and etching conditions.
Another method is to utilize methods of self-assembly at the molecular level so that devices assemble themselves in a predictable manner. This technology holds promise, but is still in its infancy.
Yet another method is to use photolithography, but to enlarge the features patterned in the photoresist so that the patterned area is large enough to compensate for estimated amounts of misalignment. This methodology can alleviate misalignment-caused problems, and has been utilized with a substantial degree of success. However, the methodology wastes valuable semiconductor real estate.
It is desired to develop new methods which can improve accuracy with which patterns are formed in photosensitive materials.